In buildings it is generally desirable to provide an exchange of air such that air from inside the building is expelled and replaced with fresh air from outside the building. In colder climates where the inside of the building is much warmer than the outside air (‘heating applications’) or in hot climates where the inside of the building is airconditioned and is much cooler than the outside air (‘cooling applications’) there is an energy cost to this. In heating applications the fresh air is typically both colder and drier than the air inside the building. Energy is required to heat and humidify the fresh air. In cooling applications the fresh air is typically both warmer and more moist than the air inside the building. Energy is required to cool and dehumidify the fresh air. The amount of energy required for heating and cooling applications can be reduced by transferring heat and moisture between the outgoing air and the incoming air. This may be done using an ERV system comprising membranes which separate flows of incoming and outgoing air. The characteristics of the membranes are an important factor in the performance of an ERV system.
Ideally a membrane in an ERV system should be: air-impermeable such that the membrane can maintain effective separation of the incoming and outgoing air flows; have a high thermal conductivity for effective heat transfer between the incoming and outgoing air flows; and provide high water vapor transport for effective transfer of moisture between the incoming and outgoing air flows but substantially block the passage of other gases. Achieving these characteristics typically favors the use of thin membranes.
In addition to the above it is desirable that the membranes be robust enough for commercial use, cost effective to produce, and compliant with any applicable regulations. At least some jurisdictions have regulations that relate to the flammability of membranes used in ERV systems. For example, UL 94 is a standard released by Underwriters Laboratories of the USA which relates to flammability of plastic materials for parts in devices and appliances. UL 94 provides additional classifications VTM-0, VTM-1, VTM-2 for thin films. UL 723 is another standard released by Underwriters Laboratories that provides a test for surface burning characteristics of building materials.
There is a need for membranes suitable for ERV applications and/or other water vapor transport applications that address some or all of these issues.